I'm investigating doing something like SecureString on .NET and use an API to encrypt and decrypt the in memory representation of sensitive data, but also doing something about in-memory copies made during either end of that process, zeroing them out afterwards.
My general question: if calling a function that returns a Swift value type, will there be any way to mutate that value directly, or will any mutation done to the result invariantly cause a CoW? It seems to me that Swift's data safety would prevent mutating the result.
For example, if I'm using an library's decrypt function that returns Data will this do what I'm intending:
var decrypted: Data = decrypt(blah) // do something with decrypted data decrypted.replaceSubrange(...) // wipe bytes in memory
or will the call to
replaceSubrange be modifying a CoW copy of the original immutable result of
decrypt(), leaving that original behind in memory after all?
Could some extension on Data allow me to break the memory safety and mutate the function result itself, zeroing its contents after I'm done?